The present invention relates to a gas recirculation flow control method and apparatus for use in an evacuation system for introducing a process gas into a vacuum chamber of semiconductor manufacturing equipment or the like and exhausting the process gas from the vacuum chamber. The gas recirculation flow control method and apparatus control the recirculation flow rate of the gas exhausted from the vacuum chamber and returned thereto through a gas recirculation line.
In semiconductor manufacturing equipment for etching, CVD process, etc., a gas is introduced into a vacuum chamber, and the gas is exhausted by reducing the pressure in the vacuum chamber to a desired pressure with a vacuum pump. With the increase in diameter of semiconductor wafers, the amount of gas used in such semiconductor manufacturing equipment is increasing. In this regard, only a part of the gas introduced into the vacuum chamber contributes to the desired reaction. The rest of the gas, which accounts for a greater part of the introduced gas, is exhausted as it is without reacting. Under these circumstances, a gas recirculation process wherein a part of gas exhausted from the vacuum chamber is returned to the vacuum chamber is carried out for the purpose of increasing the utilization efficiency of the unreacted gas. The flow rate of the gas recirculating in the gas recirculation process (i.e. recirculation ratio) is controlled by directly measuring the flow rate of the gas passing through a gas recirculation line using a mass flow controller or the like.
FIG. 1 is a diagram showing a structural example of an evacuation system in which the flow rate of a recirculating gas is controlled by directly measuring the recirculating gas flow rate using a mass flow controller as stated above. The evacuation system includes a vacuum chamber 1 into which a gas is introduced. The vacuum chamber 1 has a shower head 2. The evacuation system further includes an adaptive pressure control valve 3, a first vacuum pump suction-side gate valve 4, a first vacuum pump 5, a second vacuum pump suction-side gate valve 6, a second vacuum pump 7, a gas recirculation line 8, a gas recirculation line gate valve (on-off valve) 9, a mass flow controller 10, a first pressure sensor 11 for detecting the pressure in the vacuum chamber 1, and a second pressure sensor 12 for detecting the pressure in the upstream side of the gas recirculation line 8.
In the evacuation system having the above-described arrangement, a gas G1 is introduced into the vacuum chamber 1 through the shower head 2 at a flow rate Q1. The introduced gas is exhausted by the first vacuum pump 5 to reduce the pressure in the vacuum chamber 1 to a desired pressure. The first vacuum pump 5 is evacuated by the second vacuum pump 7 to lower the back pressure of the first vacuum pump 5 below an allowable back pressure. A part of gas G2 exhausted from the first vacuum pump 5 is returned to the vacuum chamber 1 through the gas recirculation line 8. The recirculation flow rate Q2 of gas returned to the vacuum chamber 1 is measured by the mass flow controller 10 provided in the gas recirculation line 8 and is controlled by varying the effective pumping speeds of the first vacuum pump 5 and the second vacuum pump 7, etc. on the basis of the measured flow rate Q2.
In the above-described gas recirculation flow control method, the flow rate of the recirculating gas G2 is measured directly with a mass flow controller. This method needs a differential pressure of more than about 50 kPa for the operation of the mass flow controller. In some evacuation systems, however, the differential pressure in the gas recirculation line 8 is not more than 50 kPa. Accordingly, a mass flow controller cannot be used to control the flow rate of the recirculating gas, depending upon the type of evacuation system to which the control method is applied.
The present invention was made in view of the above-described circumstances.
An object of the present invention is to provide a gas recirculation flow control method and apparatus for use in an evacuation system, which are simple in arrangement and capable of readily controlling the recirculation flow rate of a gas returning to a vacuum chamber through a gas recirculation line even when the differential pressure in the gas recirculation line is not greater than the working pressure of a mass flow controller used (i.e. not more than 50 kPa).
According to a first aspect of the present invention, there is provided a gas recirculation flow control method for use in an evacuation system having a vacuum chamber into which a gas is introduced. The evacuation system further has a first vacuum pump for exhausting the gas from the vacuum chamber and reducing the pressure in the vacuum chamber to a desired pressure, a second vacuum pump for performing evacuation to lower the back pressure of the first vacuum pump below an allowable back pressure, and a gas recirculation line for returning a part of gas exhausted from the first vacuum pump to the vacuum chamber. According to the present invention, the recirculation flow rate Q2 of the gas returning to the vacuum chamber through the gas recirculation line is controlled by adjusting the differential pressure Pdxe2x88x92Pc in the gas recirculation line by varying the effective pumping speed of the second vacuum pump using the following formula:
Q2=Cxc3x97(Pdxe2x88x92Pc) 
where: Q2 denotes the recirculation flow rate of the gas returning to the vacuum chamber through the gas recirculation line; Pc denotes the pressure in the vacuum chamber; Pd denotes the pressure in the upstream side of the gas recirculation line; and C denotes the conductance of the gas recirculation line.
By adopting the above-described arrangement in the gas recirculation flow control method for the evacuation system, the gas recirculation flow rate Q2 can be controlled simply by adjusting the differential pressure Pdxe2x88x92Pc in the gas recirculation line by varying the effective pumping speed of the second vacuum pump.
According to a second aspect of the present invention, there is provided a gas recirculation flow control method for use in an evacuation system having a vacuum chamber into which a gas is introduced. The evacuation system further has a first vacuum pump for exhausting the gas from the vacuum chamber and reducing the pressure in the vacuum chamber to a desired pressure, a second vacuum pump for performing evacuation to lower the back pressure of the first vacuum pump below an allowable back pressure, and a gas recirculation line for returning a part of gas exhausted from the first vacuum pump to the vacuum chamber. According to the present invention, the recirculation flow rate Q2 of the gas returning to the vacuum chamber through the gas recirculation line is controlled by adjusting the diferential pressure Pdxe2x88x92Pc in the gas recirculation line by varying the flow rate of a purge gas introduced upstream or inside the second vacuum pump, which consists of at least one substance used as a component of the gas introduced into the vacuum chamber, by using the following formula:
Q2=Cxc3x97(Pdxe2x88x92Pc) 
where: Q2 denotes the recirculation flow rate of the gas returning to the vacuum chamber through the gas recirculation line; Pc denotes the pressure in the vacuum chamber; Pd denotes the pressure in the upstream side of the gas recirculation line; and C denotes the conductance of the gas recirculation line.
By adopting the above-described arrangement in the gas recirculation flow control method for the evacuation system, the gas recirculation flow rate Q2 can be controlled simply by adjusting the differential pressure Pdxe2x88x92Pc in the gas recirculation line by varying the flow rate of the purge gas introduced upstream or inside the second vacuum pump.
According to a third aspect of the present invention, there is provided a gas recirculation flow control method for use in an evacuation system having a vacuum chamber into which a gas is introduced. The evacuation system further has a first vacuum pump for exhausting the gas from the vacuum chamber and reducing the pressure in the vacuum chamber to a desired pressure, a second vacuum pump for performing evacuation to lower the back pressure of the first vacuum pump below an allowable back pressure, and a gas recirculation line for returning a part of gas exhausted from the first vacuum pump to the vacuum chamber. According to the present invention, the recirculation flow rate Q2 of the gas returning to the vacuum chamber through the gas recirculation line is controlled according to a control procedure including the following steps {circle around (1)} to {circle around (3)}: {circle around (1)} introducing, in a non-recirculating state, the gas into the vacuum chamber at an arbitrary flow rate Qt, and adjusting and fixing the effective pumping speed of the first vacuum pump to an appropriate level to make the pressure Pc in the vacuum chamber equal to a desired pressure P1; {circle around (2)} changing the flow rate of the gas introduced into the vacuum chamber to Q1=Qtxc3x97(100xe2x88x92A)/100, which corresponds to an arbitrary recirculation ratio A {A=(Q2/Qtxc3x97100)}%, while fixing the effective pumping speed of the first vacuum pump at the same level as in the step {circle around (1)}; and {circle around (3)} opening the gas recirculation line, and in the gas recirculating state, adjusting the effective pumping speed of the second vacuum pump so that the pressure Pc in the vacuum chamber becomes equal to the pressure P1 obtained at the step {circle around (1)}.
By adopting the above-described arrangement in the gas recirculation flow control method for the evacuation system, the gas recirculation flow rate Q2 can be controlled simply by introducing the gas at the total flow rate Qt, adjusting the effective pumping speed of the first vacuum pump, adjusting the flow rate of the introduced gas, and adjusting the effective pumping speed of the second vacuum pump.
According to a fourth aspect of the present invention, there is provided a gas recirculation flow control method for use in an evacuation system having a vacuum chamber into which a gas is introduced. The evacuation system further has a first vacuum pump for exhausting the gas from the vacuum chamber and reducing the pressure in the vacuum chamber to a desired pressure, a second vacuum pump for performing evacuation to lower the back pressure of the first vacuum pump below an allowable back pressure, and a gas recirculation line for returning a part of gas exhausted from the first vacuum pump to the vacuum chamber. According to the present invention, the recirculation flow rate Q2 of the gas returning to the vacuum chamber through the gas recirculation line is controlled according to a control procedure including the following steps {circle around (1)} to {circle around (3)}: {circle around (1)} introducing, in a non-recirculating state, the gas into the vacuum chamber at an arbitrary flow rate Qt, and adjusting and fixing the effective pumping speed of the first vacuum pump to an appropriate level to make the pressure Pc in the vacuum chamber equal to a desired pressure P1; {circle around (2)} changing the flow rate of the gas introduced into the vacuum chamber to Q1=Qtxc3x97(100xe2x88x92A)/100, which corresponds to an arbitrary recirculation ratio A {A=(Q2/Qtxc3x97100)}%, while fixing the effective pumping speed of the first vacuum pump at the same level as in the step {circle around (1)}; and {circle around (3)} opening the gas recirculation line, and in the gas recirculating state, adjusting the flow rate of a purge gas introduced upstream or inside the second vacuum pump so that the pressure Pc in the vacuum chamber becomes equal to the pressure P1 obtained at the step {circle around (1)}, the purge gas consisting of at least one substance used as a component of the gas introduced into the vacuum chamber.
By adopting the above-described arrangement in the gas recirculation flow control method for the evacuation system, the gas recirculation flow rate Q2 can be controlled simply by introducing the gas at the total flow rate Qt, adjusting the effective pumping speed of the first vacuum pump, and adjusting the flow rate of the purge gas.
In the gas recirculation flow control method according to the first or third aspect of the present invention, the effective pumping speed of the second vacuum pump may be adjusted by a conductance control device provided upstream of the second vacuum pump.
In the gas recirculation flow control method according to the first or third aspect of the present invention, the effective pumping speed of the second vacuum pump may be adjusted by varying the number of revolutions of the second vacuum pump.
In addition, the present invention provides a gas recirculation flow control apparatus for use in an evacuation system having a vacuum chamber into which a gas is introduced. The evacuation system further has a first vacuum pump for exhausting the gas from the vacuum chamber and reducing the pressure in the vacuum chamber to a desired pressure, a second vacuum pump for performing evacuation to lower the back pressure of the first vacuum pump below an allowable back pressure, a gas recirculation line for returning a part of gas exhausted from the first vacuum pump to the vacuum chamber, a first pressure sensor for detecting the pressure in the vacuum chamber, and a second pressure sensor for detecting the pressure in the upstream side of the gas recirculation line. The gas recirculation flow control apparatus includes a gas recirculation flow control device for controlling the recirculation flow rate Q2 of the gas returning to the vacuum chamber through the gas recirculation line by adjusting the differential pressure Pdxe2x88x92Pc in the gas recirculation line by varying the effective pumping speed of the second vacuum pump using the following formula:
Q2=Cxc3x97(Pdxe2x88x92Pc) 
where: Q2 denotes the recirculation flow rate of the gas returning to the vacuum chamber through the gas recirculation line; Pc denotes the pressure detected with the first pressure sensor; Pd denotes the pressure detected with the second pressure sensor: and C denotes the conductance of the gas recirculation line.
By adopting the above-described arrangement in the gas recirculation flow control apparatus for the evacuation system, the gas recirculation flow control device can control the gas recirculation flow rate Q2 simply by adjusting the differential pressure Pdxe2x88x92Pc in the gas recirculation line, which is detected with the first and second pressure sensors, by varying the effective pumping speed of the second vacuum pump.
In addition, the present invention provides a gas recirculation flow control apparatus for use in an evacuation system having a vacuum chamber into which a gas is introduced. The evacuation system further has a first vacuum pump for exhausting the gas from the vacuum chamber and reducing the pressure in the vacuum chamber to a desired pressure, a second vacuum pump for performing evacuation to lower the back pressure of the first vacuum pump below an allowable back pressure, a gas recirculation line for returning a part of gas exhausted from the first vacuum pump to the vacuum chamber, a first pressure sensor for detecting the pressure in the vacuum chamber, and a second pressure sensor for detecting the pressure in the upstream side of the gas recirculation line. The gas recirculation flow control apparatus includes a gas recirculation flow control device for controlling the recirculation flow rate Q2 of the gas returning to the vacuum chamber through the gas recirculation line by adjusting the differential pressure Pdxe2x88x92Pc in the gas recirculation line by varying the flow rate of a purge gas introduced upstream or inside the second vacuum pump, the purge gas consisting of at least one substance used as a component of the gas introduced into the vacuum chamber, by using the following formula:
Q2=Cxc3x97(Pdxe2x88x92Pc) 
where: Q2 denotes the recirculation flow rate of the gas returning to the vacuum chamber through the gas recirculation line; Pc denotes the pressure in the vacuum chamber; Pd denotes the pressure in the upstream side of the gas recirculation line; and C denotes the conductance of the gas recirculation line.
By adopting the above-described arrangement in the gas recirculation flow control apparatus for the evacuation system, the gas recirculation flow control device can control the gas recirculation flow rate Q2 simply by adjusting the differential pressure Pdxe2x88x92Pc in the gas recirculation line, which is detected with the first and second pressure sensors, by varying the purge gas flow rate.
In addition, the present invention provides a gas recirculation flow control apparatus for use in an evacuation system having a vacuum chamber into which a gas is introduced. The evacuation system further has a first vacuum pump for exhausting the gas from the vacuum chamber and reducing the pressure in the vacuum chamber to a desired pressure, a second vacuum pump for performing evacuation to lower the back pressure of the first vacuum pump below an allowable back pressure, a gas recirculation line for returning a part of gas exhausted from the first vacuum pump to the vacuum chamber, a first pressure sensor for detecting the pressure in the vacuum chamber, a second pressure sensor for detecting the pressure in the upstream side of the gas recirculation line, and an on-off valve for selectively opening and closing the gas recirculation line. The gas recirculation flow control apparatus includes a gas recirculation flow control device for controlling the recirculation flow rate Q2 of the gas returning to the vacuum chamber through the gas recirculation line by {circle around (1)} closing the on-off valve and introducing the gas into the vacuum chamber at an arbitrary flow rate Qt, adjusting the effective pumping speed V of the first vacuum pump and fixing it to V1 to make the pressure Pc detected with the first pressure sensor equal to a desired pressure P1, {circle around (2)} and changing the flow rate of the gas introduced into the vacuum chamber to Q1=Qtxc3x97(100xe2x88x92A)/100, which corresponds to an arbitrary recirculation ratio A {A=(Q2/Qtxc3x97100)}%, while fixing the effective pumping speed V of the first vacuum pump at V1, {circle around (3)} and then opening the on-off valve and adjusting the effective pumping speed of the second vacuum pump so that the pressure Pc detected with the first pressure sensor becomes equal to the pressure P1.
By adopting the above-described arrangement in the gas recirculation flow control apparatus for the evacuation system, the gas recirculation flow control device can control the gas recirculation flow rate Q2 simply by on-off controlling the on-off valve, monitoring the pressure detected with the first pressure sensor, adjusting the flow rate of the gas introduced into the vacuum chamber, and adjusting the effective pumping speeds of the first and second vacuum pumps.
In addition, the present invention provides a gas recirculation flow control apparatus for use in an evacuation system having a vacuum chamber into which a gas is introduced. The evacuation system further has a first vacuum pump for exhausting the gas from the vacuum chamber and reducing the pressure in the vacuum chamber to a desired pressure, a second vacuum pump for performing evacuation to lower the back pressure of the first vacuum pump below an allowable back pressure, a gas recirculation line for returning a part of gas exhausted from the first vacuum pump to the vacuum chamber, a first pressure sensor for detecting the pressure in the vacuum chamber, a second pressure sensor for detecting the pressure in the upstream side of the gas recirculation line, and an on-off valve for selectively opening and closing the gas recirculation line. The gas recirculation flow control apparatus includes a gas recirculation flow control device for controlling the recirculation flow rate Q2 of the gas returning to the vacuum chamber through the gas recirculation line by {circle around (1)} closing the on-off valve and introducing the gas into the vacuum chamber at an arbitrary flow rate Qt, adjusting the effective pumping speed V of the first vacuum pump and fixing it to V1 to make the pressure Pc detected with the first pressure sensor equal to a desired pressure P1, {circle around (2)} and changing the flow rate of the gas introduced into the vacuum chamber to Q1=Qtxc3x97(100xe2x88x92A)/100, which corresponds to an arbitrary recirculation ratio A {A=(Q2/Qtxc3x97100)}%, while fixing the effective pumping speed V of the first vacuum pump at the V1, {circle around (3)} and then opening the on-off valve and adjusting the flow rate of a purge gas introduced upstream or inside the second vacuum pump so that the pressure Pc detected with the first pressure sensor becomes equal to the pressure P1, the purge gas consisting of at least one substance used as a component of the gas introduced into the vacuum chamber.
By adopting the above-described arrangement in the gas recirculation flow control apparatus for the evacuation system, the gas recirculation flow control device can control the gas recirculation flow rate Q2 simply by on-off controlling the on-off valve, monitoring the pressure detected with the first pressure sensor, adjusting the flow rate of the gas introduced into the vacuum chamber, adjusting the effective pumping speed of the first vacuum pump, and adjusting the purge gas flow rate.
In any of the above-described gas recirculation flow control apparatus, the gas recirculation flow control device preferably has the function of automatically performing an operation for controlling the recirculation flow rate of the gas.